Electric heating element



Nov. 17, 1953 w. H. ZANDER 2,659,800

ELECTRIC HEATING ELEMENT Filed Sept. 20, 1950 11 INVENTOR n fl400 AmZAV/VQER,

BY m M ATTORNEY to the accompanying drawing.

Patented Nov. 17, 1953 T D STATES PATENT OF =F-l-,Ci

Waldo H. Zander, Brookville, Ohio, 'assignoriito McGraw Electric Company, Elgin, 111., a cor- .poration of Delaware Application-September 20, 1950, Serial No. 185,8 77

aqlaims.

Thisrinvention relates to electric heating-elementslfortoasters and the like ofthe typeha'ving-a single heating face and with windings on the heating face anchored by .loops engaging spacednotches in opposing edges of a fiat insulating'form. I

The electrical resistance wire commonly employed for suchheatingelements is of ribbon form. Because of the inherent stiffness and resilience and its flat shape: it is not well suited to forming anchoring loops; betweenthe gwindings extending through, adjacent .closely spaced notches in the edges of the supporting form and anchored at the opposite face of the form from the windings. not well suited to making sharp bends at adjacent notches and frequently sharp creases are formed at the notches.

The general object of the present invention is to improve the anchoring of electrical resistance ribbon windings on a single face of a flat form at notched edges of the form.

According to the invention anchoring loops in the heating ribbon embody an axial twist, ordinarily a half twist. Such twist is found to minimize the formation of sharp creases in the ribbon at the notches and to generally improve the fit of the ribbon with the notched edges. The inherent resiliency of the ribbon may in part account for these benefits.

Desirably, the twists in the ribbon in the loops at the opposite edges of the form are in opposite directions, although this is primarily a convenience in winding.

The twisted anchoring loop formation in the heating ribbon is necessarily provided in the course of winding of the heating element. The same can be produced by hand winding merely through a slight departure, to provide the twist, from the manual technique heretofore employed. It also may be provided by the winding method and with the mechanical machine disclosed and claimed in copending application Serial No. 186,476 filed September 20, 1950 of Waldo H. Zander, Fred D. Zander and Delbert I. Wilson.

The invention will be understood by reference In such drawing:

Fig. 1 is a front view of an electric heating element according to the invention;

Fig. 2 is a corresponding rear view thereof; and,

Fig. 3 is an enlarged fragmentary rear view showing more clearly the twisted anchoring loop construction.

In particular, the flat ribbon is i As usual, the flat electrical insulating form H)- will comprise sheet mica but maycompriseether suitable insulating material. -An electrical-resistance ribbon I I isformed inspacedwindings on the front 4 face of' -theform which extend etween opposingside edges containing relatively closely spaced notches I I2 and 3. Metareye lets i4 andl5 areprov-idedin the lower-portionof the form for anchoring'th'e' ends of the ribbon and providing electric 5 terminals therefor.

At the top of the form is a metal'clampingstrip upper area. The ribbon between windings extends through adjacent notches I2 and I3 at the opposite edges of the form and is anchored by loop formations 20 and 2| at the back side of the form, best shown in Figs. 2 and 3. Such loop formations in their anchoring portions at the back side of the forms contain an axial half twist as shown and, preferably, the loop formations 20 at one edge of the form have a twist in reverse direction to the twist in loop formations 2| at the opposite edge of the form. Such twists tend to improve the fit of the ribbon with the form and take account of the fact that because of its flat form the ribbon is not adapted to undergo the sharp changes in direction required in passing from the front of the form through the notches and across the back side of the form transversely to the direction of the wind-,

ings at the front of the form. While the twisted loop formations 20 and 2| have been shown as uniform, it is found in practice the formation of the twists varies. Thus the twist may be concentrated or may be spread out along the loop formation. Such variations will depend upon the manner in which the heating elements are wound and upon the stiffness and resilience characteristics of the electrical resistance ribbon employed. The axial twist is not the result of and is not to be confused with changes in form of the ribbon incidental to change in direction at the notches.

Iclaim:

1. An electric heating element comprising a flat electric insulating form having spaced notches along opposing edges and an electric resistance ribbon having spaced windings on one face of the form extending between the opposing notched edges and connected by anchoring loops in the ribbon between adjacent windings, said anchoring loops extending through two adjacent notches in one edge of the form and passing over the opposite face of the form in anchoring portions extending between said adjacent notches, said anchoring portions being substantially straight and containing axial twists in the ribbon.

2. An electric heating element comprising a flat electric insulating form having spaced notches along opposing edges and an electric resistance ribbon having spaced windings on one face of the form extending between the opposing notched edges and connected by anchoring loops in the ribbon between adjacent windings, said anchoring loops extending through two adjacent notches in one edge of the form and passing over the opposite face of the form in anchoring portions extending between said adjacent notches, said anchoring portions being substantially straight and containing axial twists in the ribbon, the twists in the anchoring portions along one edge of the form being in a reverse direction to the twists in the anchoring portions along the opposing edge of the form.

3. An electric heating element comprising a flat electric insulating form having spaced notches along opposing edges and an electric resistance ribbon having spaced windings on one face of the form extending between the opposing notched edges and connected by anchoring loops in the ribbon between adjacent windings, said anchoring loops extending through two adjacent notches in one edge of the form and passing over the opposite face of the form in anchoring portions extending between said adjacent notches, said anchoring portions each being substantially straight and containing an axial half twist in the ribbon.

W. H. ZANDER.

References Cited in the file of this patent UNITED STATES PATENTS 

